The present disclosure relates to systems and methods for large-scale production of carbon nanotube materials.
Nanotube growth process involves significant volume expansion. For example, a volume expansion of 50˜5,000 times of the starting materials has been observed. Due to the volume expansion, the corresponding density of the solid materials can drop about 1˜2 orders of magnitude. The change in density typically results in significant differences in the fluidization properties of the particles. Therefore, it remains a challenge to provide continuous production of carbon nanotubes of various densities.
Since the process for nanotube growth accompanies by a gradual loss of catalysts activity and decreased conversion, new catalysts must be supplied to the reaction system in order to increase the conversion for continuous production of carbon nanotubes. However, the newly added catalysts and the crude products have very different densities, and require different fluidization conditions. When the superficial velocity is high, the initial low-density products, such as agglomerates, can migrate out of the reactor with the flow of the gases. This will result in several disadvantages, for example, insufficient reaction time, low growth ratio per gram of catalyst and low efficiency of catalyst utilization. When the superficial velocity is low, the fresh catalysts cannot be used efficiently, which will result in low productivity, poor fluidization condition, elutriation, poor heat transport, and coagulation of the solid particles.
Maintaining proper fluidization conditions is critical for the production of carbon nanotubes. During the initial growth stage of carbon nanotubes, poor catalyst fluidization can lead to the formation of aggregates or chunks, which result in the blockage of the reactor. In the later growth stage of carbon nanotubes, the density of the materials decreases drastically. The particles are loose and easily aggregated together. The coagulation of the particles can result in poor fluidization conditions. There is therefore a need for improved fluidization conditions for all particles in the reaction system in a continuous production of carbon nanotubes.